This invention relates to laser drilling of components, particularly, although not exclusively, the drilling of holes in gas turbine components such as hollow turbine blades.
The laser drilling of holes such as film-cooling holes into internal passages of turbine blades has been known for some time. However, a problem that commonly arises is that of preventing the laser beam from damaging the wall of the passage opposite to where the laser beam breaks through. Another problem that arises is that of preventing material sputtered or vaporised by the beam from being deposited on the inner surfaces of the passage.
Attempts have been made to insert barriers in the passages, and indeed in passages which are relatively large and do not have complicated shapes it may be possible to use solid barriers.
Attempts have been made to pour molten wax into the passage prior to laser drilling so that on solidification it provides a useful barrier. However, a problem arises when a series of holes close together in a blade is being drilled. It is found that the solid wax in the passage can melt in the vicinity of a hole being drilled and can form an unwanted cavity under the site of a second hole to be drilled, thus reducing resistance to laser strike-through when that second hole is subsequently drilled.